Method for purging condensate from a charge air cooler

ABSTRACT

Methods and systems are provided for cleaning out condensate stored at a charge air cooler. In response to increased condensate accumulation at a charge air cooler, airflow through the engine is increased to purge the condensate while an engine actuator is adjusted to maintain engine torque. Combustion stability issues of engine cylinders are addressed by adjusting fueling of each cylinder individually during condensate ingestion.

FIELD

The present application relates to methods and systems for purgingcondensate from a charge air cooler without degrading combustionstability.

BACKGROUND/SUMMARY

Turbocharged and supercharged engines may be configured to compressambient air entering the engine in order to increase power. Compressionof the air may cause an increase in air temperature, thus, a charge aircooler may be utilized to cool the heated air thereby increasing itsdensity and further increasing the potential power of the engine.Ambient air from outside the vehicle travels across the CAC to coolintake air passing through the inside of the CAC. Condensate may form inthe CAC when the ambient air temperature decreases, or during humid orrainy weather conditions, where the intake air is cooled below the waterdew point. Condensate may collect at the bottom of the CAC, or in theinternal passages, and cooling turbulators. When torque is increased,such as during acceleration, increased mass air flow may strip thecondensate from the CAC, drawing it into the engine and increasing thelikelihood of engine misfire.

Example approaches of addressing combustion issues (e.g., misfire)resulting from condensate ingestion involve avoiding condensatebuild-up. However, the inventors herein have recognized potential issueswith such methods. Specifically, while some methods may reduce or slowcondensate formation in the CAC, condensate may still build up overtime. If this build-up cannot be stopped, ingestion of the condensateduring acceleration may cause engine misfire. In addition, based on theengine speed-load condition, as well as the configuration of the engine(e.g., based on whether the engine is V-engine with distinct banks or anin-line engine), some cylinders may receive more condensate than others,rendering them more prone to combustion issues than others. Otherexample approaches of addressing the combustion issues involve trappingand/or draining the condensate from the CAC. While this may reducecondensate levels in the CAC, condensate is moved to an alternatelocation or reservoir, which may be subject to other condensate problemssuch as freezing and corrosion. Further, the reservoir may add componentcost and complexity. Still other approaches purge condensate from theCAC opportunistically when engine airflow increases, such as during adriver pedal tip-in. However, the tip-in may not occur at the same timethat condensate purging is required. In the interim, condensate maycontinue to be ingested in the engine, degrading combustion.

In one example, the above described issues may be at least partlyaddressed by a method for purging condensate from the CAC during vehicleoperating conditions. The method may comprise: in response to condensatelevel in a charge air cooler, adjusting fuel injection timing whileincreasing engine airflow to a level greater than requested by a vehicleoperator. In this way, one or more engine cylinders may be temporarilyoperated in a lean stratified mode to purge the condensate while theoperation of other engine cylinders is adjusted to maintain astoichiometric exhaust air-fuel ratio.

In one example, an engine system may include a charge air cooler coupleddownstream of a compressor and upstream of an intake throttle. Duringengine operation, condensate may collect at the charge air cooler. Inresponse to condensate levels being higher than a threshold, purgingconditions may be considered met and a clean-out cycle may be initiatedto remove the condensate. In particular, the fuel injection timing ofone or more engine cylinders may be shifted from an injection timingthat provides a homogeneous cylinder air-fuel charge that is ignitedwith spark to an alternate injection timing that provides at least somestratified cylinder air-fuel charge that is ignited with spark. Byoperating at least some cylinders in a lean stratified mode, an engineairflow level can be increased to or above a blow-off level wherecondensate is blown into the engine.

As an example, cylinders that are less sensitive to water ingestion(that is, cylinders less prone to ingestion induced misfires) may beoperated in the lean stratified mode while the remaining cylinders (thatis, cylinders more prone to ingestion induced misfires) are operatedrich such that an overall exhaust air-fuel ratio is maintained at oraround stoichiometry. The degree of leanness may be adjusted based onthe amount of condensate at the cylinder so that the engine airflow canbe sufficiently increased. The water ingestion sensitivity of thecylinders may be determined based on engine speed-load conditions at thetime of the purging, an amount of condensate received in each cylinder,a configuration of the engine, cylinder firing order, etc. Adjusting thefuel injection timing of a cylinder to transition from the homogenousmode of cylinder combustion to the lean stratified mode of cylindercombustion may include shifting fuel injection timing from an intakestroke to a compression stroke, increasing a number of injections percombustion event, adjusting a split ratio of fuel delivery split betweenthe injections, etc.

In this way, condensate may be periodically cleaned from a charge aircooler by operating one or more cylinders in a lean stratified mode. Byadjusting the fuel injection timing of a cylinder such that an airflowlevel is increased to a level that enables blowing off of condensatefrom the CAC, purging can be performed without waiting for a tip-inevent. At the same time, by adjusting the fuel injection timing toproviding a stratified fuel injection, a rich environment can bemaintained in the vicinity of the cylinder's spark plug, allowing for amore stable combustion. By adjusting the fuel injection timing so thatan overall exhaust air-fuel ratio is maintained at stoichiometry, engineperformance during the purging is improved.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example engine system including acharge air cooler.

FIG. 2 shows an example combustion chamber of the engine system of FIG.1.

FIG. 3 shows a high level flow chart of a method for adjusting enginefueling during purging of condensate from a charge air cooler (CAC)based on each cylinder's water ingestion sensitivity.

FIG. 4 shows a high level flow chart of a method for adjusting fuelinjection during purging of condensate from a charge air cooler (CAC) totemporarily operate one or more engine cylinders in a lean stratifiedmode.

FIG. 5 shows an example look-up table that may be used to store dataregarding water ingestion sensitivity of engine cylinders.

FIG. 6 shows a high level flow chart of a method for determining adegree of richness for the “weak” cylinders based on combustionstability limits and adjusting the degree of leanness of the “strong”cylinders in accordance.

FIG. 7 shows a high level flow chart of a method for determining adegree of leanness of the “strong” cylinders based on a lean stratifiedmode limit and adjusting the degree of richness for the “weak” cylindersin accordance.

FIG. 8 shows a map depicting a relationship between the strength of thestrong cylinders and the degree of leanness required, and a weakness ofthe weak cylinders and the degree of richness required.

FIG. 9 shows a graphical example of adjusting fuel injection to one ormore engine cylinders during purging based on their respective wateringestion sensitivities.

FIG. 10 shows a graphical example of adjusting air-fuel ratio of one ormore engine cylinders during purging to operate at least some cylindersin a lean stratified mode.

DETAILED DESCRIPTION

The following description relates to systems and methods for purgingcondensate from a charge air cooler (CAC) to an engine system, such asthe system of FIGS. 1-2. During the purging, engine airflow may betemporarily increased, while an engine actuator, such as spark timing,is adjusted responsive to the condensate flow. CAC condensate purgingmay occur in response to elevated condensate levels. An enginecontroller may be configured to perform a control routine, such as theroutine of FIG. 3, to adjust fueling of each cylinder during the purgingbased on each cylinder's water ingestion sensitivity (FIG. 5).Alternatively, the controller may perform the example routine of FIG. 4to adjust the fuel injection timing so that a lean stratified mode ofcylinder combustion is provided. The controller may operate one or morecylinders rich while operating other cylinders lean (FIG. 6-8) with adegree of richness and leanness adjusted to maintain exhaust emissions.In either case, engine airflow is increased to blow off condensate intothe engine cylinder, thereby reducing the occurrence of ingestioninduced misfire events. Example fuel adjustments that may be used tostrip condensate from a CAC and purge it into an engine intake are shownwith reference to FIGS. 9-10.

FIG. 1 is a schematic diagram showing an example engine 10, which may beincluded in a propulsion system of an automobile. The engine 10 is shownwith four cylinders 30. However, other numbers of cylinders may be usedin accordance with the current disclosure. Engine 10 may be controlledat least partially by a control system including controller 12, and byinput from a vehicle operator 132 via an input device 130. In thisexample, input device 130 includes an accelerator pedal and a pedalposition sensor 134 for generating a proportional pedal position signalPP. Each combustion chamber (e.g., cylinder) 30 of engine 10 may includecombustion chamber walls with a piston (discussed at FIG. 2) positionedtherein. The pistons may be coupled to a crankshaft 40 so thatreciprocating motion of the piston is translated into rotational motionof the crankshaft. Crankshaft 40 may be coupled to at least one drivewheel of a vehicle via an intermediate transmission system (not shown).Further, a starter motor may be coupled to crankshaft 40 via a flywheelto enable a starting operation of engine 10.

Combustion chambers 30 may receive intake air from intake manifold 44via intake passage 42 and may exhaust combustion gases via exhaustmanifold 46 to exhaust passage 48. Intake manifold 44 and exhaustmanifold 46 can selectively communicate with combustion chamber 30 viarespective intake valves and exhaust valves (not shown). In someembodiments, combustion chamber 30 may include two or more intake valvesand/or two or more exhaust valves.

Fuel injectors 66 are shown coupled directly to combustion chamber 30for injecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12. In this manner, fuel injector 66provides what is known as direct injection of fuel into combustionchamber 30; however it will be appreciated that port injection is alsopossible. Fuel may be delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail.

Intake passage 42 may include throttle 21 having a throttle plate 22 toregulate air flow to the intake manifold. In this particular example,the position (TP) of throttle plate 22 may be varied by controller 12 toenable electronic throttle control (ETC). In this manner, throttle 21may be operated to vary the intake air provided to combustion chamber 30among other engine cylinders. In some embodiments, additional throttlesmay be present in intake passage 42, such as a throttle upstream of thecompressor (not shown).

Further, in the disclosed embodiments, an exhaust gas recirculation(EGR) system may route a desired portion of exhaust gas from exhaustpassage 48 to intake passage 42 via EGR passage 140. The amount of EGRprovided to intake passage 42 may be varied by controller 12 via EGRvalve 142. Under some conditions, the EGR system may be used to regulatethe temperature of the air and fuel mixture within the combustionchamber. FIG. 1 shows a high pressure EGR system where EGR is routedfrom upstream of a turbine of a turbocharger to downstream of acompressor of a turbocharger. In other embodiments, the engine mayadditionally or alternatively include a low pressure EGR system whereEGR is routed from downstream of a turbine of a turbocharger to upstreamof a compressor of the turbocharger. When operable, the EGR system mayinduce the formation of condensate from the compressed air, particularlywhen the compressed air is cooled by the charge-air-cooler, as describedin more detail below.

Engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 162arranged along intake manifold 44. For a turbocharger, compressor 162may be at least partially driven by a turbine 164, via, for example ashaft, or other coupling arrangement. The turbine 164 may be arrangedalong exhaust passage 48. Various arrangements may be provided to drivethe compressor. For a supercharger, compressor 162 may be at leastpartially driven by the engine and/or an electric machine, and may notinclude a turbine. Thus, the amount of compression provided to one ormore cylinders of the engine via a turbocharger or supercharger may bevaried by controller 12.

Further, exhaust passage 48 may include wastegate 171 for divertingexhaust gas away from turbine 164. Additionally, intake passage 42 mayinclude a compressor recirculation valve (CRV) 27 configured to divertintake air around compressor 162.

Wastegate 171 and/or CRV 27 may be controlled by controller 12 to beopened when a lower boost pressure is desired, for example.

Intake passage 42 may further include charge air cooler (CAC) 80 (e.g.,an intercooler) to decrease the temperature of the turbocharged orsupercharged intake gases. In some embodiments, charge air cooler 80 maybe an air to air heat exchanger. In other embodiments, charge air cooler80 may be an air to liquid heat exchanger. CAC 80 may be a variablevolume CAC wherein the charge air cooler 80 includes a valve toselectively modulate the amount and flow velocity of intake airtraveling through the charge air cooler 80 in response to condensationformation within the charge air cooler as well as engine loadconditions.

In both variable and non-variable embodiments of CAC 80, purging ofstored condensate can be enabled in response to the condensate levelbeing higher than a threshold. As elaborated herein, purging may beperformed opportunistically during conditions when engine airflow ishigher, such as during a tip-in event. Additionally, an engine airflowmay be actively increased, for example, by increasing an opening of thethrottle, to purge the condensate while an engine actuator, for examplespark timing, is adjusted to maintain engine torque output. As furtherelaborated herein, purging may also be enabled by temporarily operatingthe engine in a stratified mode. Specifically, fuel injection timing toone or more engine cylinders may be adjusted such that at least somecylinders are operated in a lean stratified mode. The degree of leannessmay be adjusted such that the engine airflow level (mass airflow rate)is at a level that causes condensate blow-off. By raising the massairflow rate high enough, above the mass flow rate needed to start topurge the condensate from the CAC, but not high enough to cause misfireand poor combustion, the condensate can be removed without poorcombustion side effects.

As such, the water ingestion sensitivity of the engine cylinders mayvary with some cylinders having a higher water ingestion sensitivity(e.g., more prone to ingestion induced misfires) and other cylindershaving a lower water ingestion sensitivity (e.g., less prone toingestion induced misfires). The variation may be due to, for example,engine geometry, location of the cylinder on the engine bank, and firingorder. In other words, the shape of the manifold may typically determinewhich cylinder(s) receive the condensate. For example, in an in-lineengine, cylinders located furthest from the CAC may be more sensitive towater ingestion than cylinders located closest to the CAC. As anotherexample, in a V-engine (e.g., a V-6 arrangement), cylinders locatedfurthest from the throttle inlet may receive more condensate thancylinders positioned closer to the throttle inlet. For example, the leftbank may experience more water ingestion if the throttle body ispointing to the left bank. As such, since water is denser than air, thecondensate does not bend around turns and consequently can hit the endof the intake and run into the furthest cylinders. As yet anotherexample, cylinders on one bank may be more sensitive than the cylinderson the other bank. Further still, the presence of additional bends inthe intake can substantially flow a majority of the purged condensateinto a specific cylinder.

In some embodiments, the water ingestion sensitivity may correlate withthe amount (or percentage) of condensate the cylinders are likely toreceive. This is because when the engine airflow is increased to purgethe condensate, condensate amounts may unequally flow to the enginecylinders with some cylinders receiving higher amounts of condensatethan other cylinders. Therein, cylinders receiving larger amounts ofcondensate may be more prone to misfires and other combustion issues(that is, have higher water ingestion sensitivity) while other cylindersreceiving smaller amounts of condensate may be less prone to misfiresand other combustion issues (that is, have lower water ingestionsensitivity).

The water ingestion sensitivity may also vary with engine speed-loadconditions. For example, a particular cylinder (or set of cylinders) maybe more sensitive to water ingestion at low engine speed-load conditionswhile an alternate cylinder (or set of cylinders) are more sensitive towater ingestion at low-mid engine speed-load conditions. In an alternateexample, water ingestion sensitivities of all the cylinders may be lowerat low engine speed-load conditions due to the intake air mass flowbeing too low at the low engine speed and/or low engine load conditionsto carry water from the CAC to the intake manifold. In another example,at high engine speed and high engine load conditions, the wateringestion sensitivity of all the cylinders may be higher due to thehigher air mass flow rates that strip the condensate from the CAC andcarry it into the intake manifold. Further still, if the airflow issufficient enough, at high engine speed and low engine load conditions,the cylinders may be most sensitive to water ingestion due to poorcombustion stability of the cylinders at the light load conditions.Since the shape of the manifold largely determines which cylindersingest the condensate, in another example, a particular cylinder (or setof cylinders) may be more sensitive to water ingestion at high enginespeed-load conditions while an alternate cylinder (or set of cylinders)is more sensitive to water ingestion at low-mid engine speed-loadconditions.

Differences in water ingestion sensitivity between the cylinders may beinferred or estimated based on operating conditions. Alternatively, theengine may be characterized during engine testing using a dynamometer.Specifically, during engine testing, water vapor may be introduced intothe air intake system and cylinder pressure data may be utilized tocharacterize the effect of the water. The cylinders may then be mappedto identify the “weak” cylinders with high water ingestion sensitivityand the “strong” cylinders with low water ingestion sensitivity. The mapmay be stored in the controller's memory (for example, as a function ofengine speed-load conditions), and retrieved during a purging operation.As elaborated herein, to compensate for the difference in wateringestion sensitivity, and/or the unequal condensate flow along thecylinders, during purging, the fueling of each cylinder may be adjustedbased on the water ingestion sensitivity of each cylinder. For example,the “weak” cylinders (having higher water ingestion sensitivity) may beoperated rich while the “strong” cylinders (having lower water ingestionsensitivity) are operated lean. A degree of leanness of the leanoperating cylinders may be adjusted so that the engine airflow can beincreased to or above a blow-off level that enables condensate to bepurged from the CAC. A degree of richness of the rich operatingcylinders is then adjusted based on the degree of leanness of the leanoperating cylinders so that an overall exhaust air-fuel ratio (as seenby an exhaust catalyst) may be maintained at or around (e.g.,oscillating around) stoichiometry. In one example, where the wateringestion sensitivity is induced by the unequal condensate ingestion,the controller may operate cylinders receiving more condensate richwhile operating cylinders receiving less condensate lean, with anoverall exhaust air-fuel ratio maintained at or around stoichiometry. Byadjusting the fueling of each cylinder taking into account eachcylinder's water ingestion sensitivity, condensate purging can beachieved without degrading cylinder combustion and without incurringfrequent misfires.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10 for performing variousfunctions to operate engine 10, in addition to those signals previouslydiscussed, including measurement of inducted mass air flow (MAF) frommass air flow sensor 120; engine coolant temperature (ECT) fromtemperature sensor 112, shown schematically in one location within theengine 10; a profile ignition pickup signal (PIP) from Hall effectsensor 118 (or other type) coupled to crankshaft 40; the throttleposition (TP) from a throttle position sensor, as discussed; andabsolute manifold pressure signal, MAP, from sensor 122, as discussed.Engine speed signal,

RPM, may be generated by controller 12 from signal PIP. Manifoldpressure signal MAP from a manifold pressure sensor may be used toprovide an indication of vacuum, or pressure, in the intake manifold 44.Note that various combinations of the above sensors may be used, such asa MAF sensor without a MAP sensor, or vice versa. During stoichiometricoperation, the MAP sensor can give an indication of engine torque.Further, this sensor, along with the detected engine speed, can providean estimate of charge (including air) inducted into the cylinder. In oneexample, sensor 118, which is also used as an engine speed sensor, mayproduce a predetermined number of equally spaced pulses every revolutionof the crankshaft 40.

Other sensors that may send signals to controller 12 include atemperature sensor 124 at the outlet of the charge air cooler 80, and aboost pressure sensor 126. Still other sensors include knock sensor 90coupled to the engine block. The controller may infer condensateconsumption at one or more engine cylinders during condensate purgingbased on the knocking frequency of the cylinders. Other sensors notdepicted may also be present, such as a sensor for determining theintake air velocity at the inlet of the charge air cooler, and othersensors, as described at FIG. 2. In some examples, storage mediumread-only memory 106 may be programmed with computer readable datarepresenting instructions executable by processor 102 for performing themethods described below as well as other variants that are anticipatedbut not specifically listed. Example routines are described herein atFIGS. 3-4.

Referring now to FIG. 2, a detailed embodiment of one cylinder of theengine of FIG. 1 is shown. As such, components previously introduced inFIG. 1 may be numbered the same in FIG. 2 and will not be re-introduced.Engine 10 includes combustion chamber (cylinder) 30 and cylinder walls32 with piston 36 positioned therein and connected to crankshaft 40.Combustion chamber 30 is shown communicating with intake manifold 46 andexhaust manifold 48 via respective intake valve 52 and exhaust valve 54.Each intake and exhaust valve may be operated by an intake cam 51 and anexhaust cam 53. The opening and closing time of exhaust valve 54 may beadjusted relative to crankshaft position via cam phaser 58. The openingand closing time of intake valve 52 may be adjusted relative tocrankshaft position via cam phaser 59. The position of intake cam 51 maybe determined by intake cam sensor 55. The position of exhaust cam 53may be determined by exhaust cam sensor 57. In this way, controller 12may control the cam timing through phasers 58 and 59. Variable camtiming (VCT) may be either advanced or retarded, depending on variousfactors such as engine load and engine speed (RPM). Fuel injector 66 isshown positioned to inject fuel directly into combustion chamber 30,which is known to those skilled in the art as direct injection.Alternatively, fuel may be injected to an intake port to provide portinjection of the fuel. Fuel injector 66 delivers liquid fuel inproportion to the pulse width of signal FPW from controller 12. Fuel isdelivered to fuel injector 66 by a fuel system (not shown) including afuel tank, fuel pump, and fuel rail (not shown). Fuel injector 66 issupplied operating current from driver 68 which responds to controller12. In one example, a high pressure, dual stage, fuel system is used togenerate higher fuel pressures. In addition, intake manifold 46 is showncommunicating with optional electronic throttle 62 which adjusts aposition of throttle plate 64 to control air flow from intake boostchamber 44. Compressor 162 draws air from air intake 42 to supply intakeboost chamber 44. Exhaust gases spin turbine 164 which is coupled tocompressor 162 which compresses air in boost chamber 44. Variousarrangements may be provided to drive the compressor. For asupercharger, compressor 162 may be at least partially driven by theengine and/or an electric machine, and may not include a turbine. Thus,the amount of compression provided to one or more cylinders of theengine via a turbocharger or supercharger may be varied by controller12. Turbocharger waste gate 171 is a valve that allows exhaust gases tobypass turbine 164 via bypass passage 173 when turbocharger waste gate171 is in an open state. Substantially all exhaust gas passes throughturbine 164 when waste gate 171 is in a fully closed position.

An exhaust gas recirculation (EGR) system may route a desired portion ofexhaust gas from exhaust manifold 48 to intake boost chamber 44 via EGRpassage 140. The amount of

EGR provided to intake boost chamber 44 may be varied by controller 12via EGR valve 172. Under some conditions, the EGR system may be used toregulate the temperature of the air and fuel mixture within thecombustion chamber. The EGR system may induce the formation ofcondensate from the compressed air, particularly when the compressed airis cooled by the charge air cooler, as described in more detail below.Specifically, EGR contains a large amount of water as it is a combustionby-product. Since EGR is at a relatively high temperature and contains alot of water, the dew-point temperature may also be relatively high.Consequently, condensate formation from EGR can be much higher thancondensate formation from compressing air and lowering it to thedew-point temperature. Intake boost chamber 44 may further includecharge air cooler (CAC) 166 (e.g., an intercooler) to decrease thetemperature of the turbocharged or supercharged intake gases. In someembodiments, CAC 166 may be an air to air heat exchanger. In otherembodiments, CAC 166 may be an air to liquid heat exchanger. CAC 166 mayinclude a valve to selectively modulate the flow velocity of intake airtraveling through the charge air cooler 166 in response to condensationformation within the charge air cooler.

Hot charge air from the compressor 162 enters the inlet of the CAC 166,cools as it travels through the CAC 166, and then exits to pass thoughthe throttle 62 and into the engine intake manifold 46. Ambient air flowfrom outside the vehicle may enter engine 10 through a vehicle front endand pass across the CAC, to aid in cooling the charge air. Condensatemay form and accumulate in the CAC when the ambient air temperaturedecreases, or during humid or rainy weather conditions, where the chargeair is cooled below the water dew point. When the charge air includesrecirculated exhaust gasses, the condensate can become acidic andcorrode the CAC housing. The corrosion can lead to leaks between the aircharge, the atmosphere, and possibly the coolant in the case ofwater-to-air coolers. To reduce the accumulation of condensate and riskof corrosion, condensate may be collected at the bottom of the CAC, andthen be purged into the engine during selected engine operatingconditions, such as during acceleration events. However, if thecondensate is introduced at once into the engine during an accelerationevent, there may be an increase in the chance of engine misfire orcombustion instability (in the form of late/slow burns) due to theingestion of water. Thus, as elaborated herein with reference to FIGS.3-4, condensate may be purged from the CAC to the engine undercontrolled conditions. This controlled purging may help to reduce thelikelihood of engine misfire events. In one example, condensate may bepurged from the CAC using increased airflow.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of turbine 164. Alternatively, a two-stateexhaust gas oxygen sensor may be substituted for UEGO sensor 126.

In some examples, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle. The hybrid vehicle may have a parallelconfiguration, series configuration, or variation or combinationsthereof. Further, in some examples, other engine configurations may beemployed, for example a diesel engine.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 46, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. Spark ignition timing may be controlled such that thespark occurs before (advanced) or after (retarded) the manufacturer'sspecified time. For example, spark timing may be retarded from maximumbreak torque (MBT) timing to control engine knock or advanced under highhumidity conditions. In particular, MBT may be advanced to account forthe slow burn rate. During the expansion stroke, the expanding gasespush piston 36 back to BDC. Crankshaft 40 converts piston movement intoa rotational torque of the rotary shaft. Crankshaft 40 may be used todrive alternator 168. Finally, during the exhaust stroke, the exhaustvalve 54 opens to release the combusted air-fuel mixture to exhaustmanifold 48 and the piston returns to TDC. Note that the above is shownmerely as an example, and that intake and exhaust valve opening and/orclosing timings may vary, such as to provide positive or negative valveoverlap, late intake valve closing, or various other examples.

Controller 12 receives various signals from sensors coupled to engine10, including those signals previously discussed. Controller 12 maycommunicate with various actuators, which may include engine actuatorssuch as fuel injectors, an electronically controlled intake air throttleplate, spark plugs, camshafts, etc. Various engine actuators may becontrolled to provide or maintain torque demand as specified by thevehicle operator 132. These actuators may adjust certain engine controlparameters including: variable cam timing (VCT), the air-to-fuel ratio(AFR), alternator loading, spark timing, throttle position, etc. Forexample, when an increase in PP is indicated (e.g., during a tip-in)from pedal position sensor 134, torque demand is increased.

Now turning to FIG. 3, an example routine 300 for purging condensatefrom a CAC while adjusting fueling of engine cylinders to compensate forunequal condensate flow and variations in water ingestion sensitivity isdepicted. By increasing engine airflow while adjusting the fueling ofthe cylinders based on their condensate sensitivity, the condensate canbe purged without increasing the frequency of misfires or othercombustion issues.

At 302, the routine includes estimating and/or measuring engineoperating conditions. These may include driver torque demand (based on apedal position), engine speed (Ne) and load, ECT, boost, ambienttemperature, MAF, MAP, EGR amount, air-fuel ratio (A/F), ambienthumidity, ambient pressure, BP, engine temperature, exhaust catalysttemperature, CAC conditions (inlet and outlet temperature, inlet andoutlet pressure, flow rate through the CAC, etc.) and other parameters.

At 304, the routine includes determining a level (or amount) ofcondensate stored at the CAC. This may include retrieving details suchas ambient air temperature, ambient air humidity, inlet and outletcharge air temperature, and inlet and outlet charge air pressure from aplurality of sensors and using the variables to determine the amount ofcondensate formed in the CAC. The condensate level may be estimatedbased on each of mass air flow, ambient temperature, CAC outlettemperature, CAC pressure, ambient pressure, and an EGR amount. Thecondensate level may be further based on input from a humidity sensor.In one example, at 306, condensate levels at the CAC are based on amodel that computes the rate of condensate formation within the CACbased on ambient temperature, CAC outlet temperature, mass flow, EGR,humidity, etc. Therein, the ambient temperature and humidity values areused to determine the dew point of the intake air, which may be furtheraffected by the amount of EGR in the intake air (e.g., EGR may have adifferent humidity and temperature than the air from the atmosphere).The difference between the dew point and the CAC outlet temperature mayindicate whether condensation will form within the cooler, and the massair flow may affect how much condensation actually accumulates withinthe cooler.

In another example, at 308, condensate levels are mapped to CAC outlettemperature and a ratio of CAC pressure to ambient pressure.Alternatively, the condensation formation value may be mapped to CACoutlet temperature and engine load. Engine load may be a function of airmass, torque, accelerator pedal position, and throttle position, andthus may provide an indication of the air flow velocity through the CAC.For example, a moderate engine load combined with a relatively cool CACoutlet temperature may indicate a high condensation formation value, dueto the cool surfaces of the CAC and relatively low intake air flowvelocity. In one example, the map may include a modifier of ambienttemperature. In another example, a pressure ratio of the CAC to theambient pressure may be used to estimate condensation formation.Therein, engine load may be normalized and estimated in the intakemanifold (behind the throttle) so it might be a lower pressure than inthe CAC.

At 310, the determined condensate level may be compared to a thresholdlevel to determine if purging conditions have been met. The thresholdlevel may be an upper threshold of condensate storage. If the condensatelevel is not higher than the threshold level, then at 312, it may bedetermined that purging conditions have not been met and a clean outcycle is not initiated.

If the condensate level is higher than the threshold level, then at 314,the routine includes determining the water ingestion sensitivity of theengine cylinders at the given operating conditions. In one example, thewater ingestion sensitivity of the engine cylinders may have beendetermined during engine testing (e.g., based on output from adynamometer) and stored in the controller's memory in a look-up table(e.g., as a function of engine speed-load). The controller may thenretrieve the data from the look-up table. An example look-up table isshown at 500 in FIG. 5. Therein, the engine is an inline 4 cylinderengine having a firing order of 1, 3, 4, 2. Based on the testing data,for a given engine speed-load condition, cylinders having higher wateringestion sensitivity may be marked as “weak” while cylinders havinglower water ingestion sensitivity may be marked as “strong”. Forexample, at low engine speed and low engine load conditions, allcylinders are considered strong since the mass airflow at theseconditions is not high enough to strip condensate from the CAC. Incomparison, at high engine speed and low engine load conditions, all thecylinders may be considered weak since the mass airflow at theseconditions is high enough to strip condensate from the CAC but the lowengine load leads to poor combustion stability. In another example,during conditions when the cylinders are sufficiently hot, none of thecylinders may be considered weak.

It will be appreciated that in alternate example, a given set ofcylinders may be consistently prone to condensate ingestion across theengine speed-load range. This may be because, generally, condensateingestion is a problem incurred mostly at high engine speed and/or highengine load conditions where the mass air flow is high enough to stripcondensate out of the CAC. Additionally, at light loads, with low orhigh engine speeds, it may be unlikely that the air mass flow rate ishigh enough to strip the condensate. In still further engineembodiments, a device like a charge motion control valve, or plenumcommunication valve, may be included in the intake manifold which maychange manifold dynamics enough to affect condensate distribution in theintake manifold.

At 316, the strong cylinders with the lower water ingestion sensitivitymay be selected for lean engine operation. Further, a degree of leannessof the selected cylinders may be adjusted to increase the engine airflowto or above a threshold level (herein also referred to as a blow-offlevel) that enables condensate purging. As such, the engine airflow maybe increased by increasing an opening of an intake throttle based on thedegree of leanness requested. The degree of leanness may be selected toprovide an increased engine airflow level that is based on the estimatedcondensate level at the charge air cooler and engine operatingconditions. For example, as the condensate level increases, a degree ofleanness may be scheduled to increase engine airflow to or above athreshold level that is required to strip water from the CAC at acontrolled rate. That is, by operating one or more of the enginecylinders lean (herein, by operating the strong cylinders lean), engineairflow level is increased based on the condensate level in the chargeair cooler, as well as the rate at which the condensate should beintroduced to the engine (which in turn is based on the rate it caningest the condensate while minimizing impact on combustion), to orabove a blow-off level required to purge condensate from the charge aircooler. By raising the airflow rate, a condensate airflow strippingvelocity in the CAC is raised, which purges the condensate into theengine.

At 318, the routine includes selecting the weak cylinders with thehigher water ingestion sensitivity for rich engine operation.Specifically, the degree of richness of the rich operating cylinders maybe adjusted based on the degree of leanness of the lean operatingcylinders so as to maintain an overall exhaust air-fuel ratiooscillating around stoichiometry.

As such, during the purging, unequal amounts of condensate may flow fromthe charge air cooler to among the cylinders. The variation may belargely a function of the geometry of the intake manifold as well as thephysics of the way the condensate flows through the manifold. The amountof condensate flowed into each engine cylinder may vary based on one ormore of engine speed, engine geometry (e.g., inline engine versusV-engine, 4-cylinder engine versus 6-cylinder engine, etc.), cylinderposition on engine block (e.g., close to CAC or further from CAC), andcylinder firing order. For example, cylinders positioned farther fromthe CAC outlet and throttle inlet may receive more condensate during thepurging than cylinders positioned closer to the CAC outlet or throttleinlet. In particular, due to the momentum of the flowing of the watertowards the rear of the intake manifold, the condensate may impinge onthe rear of the manifold, and be directed into the rear cylinders. Asanother example, cylinders may receive more condensate at higher enginespeed-load conditions and less at lower engine speed-load conditions. Inaddition to the manifold and combustion system design, this unequaldistribution of purged condensate among the engine cylinders may be atleast partly responsible for the differences in cylinder water ingestionsensitivity. The water ingestion sensitivity may also be due to otherengine operating conditions. For example, if a particular cylinderreceives more residuals, and that cylinder also receives above averageamounts of condensate, it may misfire first.

A degree of enrichment of the cylinders fueled rich and a degree ofenleanment of the cylinders fueled lean may be adjusted based on anumber of cylinders with the higher water ingestion sensitivity and anumber of cylinders with the lower water ingestion sensitivity, andfurther based on the amount of condensate being purged, to maintain theexhaust air-fuel ratio (as received at an exhaust emission controldevice, such as an exhaust three-way catalyst).

As elaborated below at FIG. 6, the adjusting may include firstdetermining the degree of leanness of the strong cylinders to provide anengine airflow level that enables condensate blow-off and then adjustingthe degree of richness of the weak cylinders to provide an overallstoichiometric exhaust air-fuel ratio. In other words, the degree ofleanness of the weak cylinders may be the limiting factor. In alternateexamples, however, the adjusting may include first determining thedegree of richness required to address the combustion stability issues(e.g., propensity for misfires) of the weak cylinders and then adjustingthe degree of leanness of the strong cylinders to provide an overallstoichiometric exhaust air-fuel ratio. In other words, the degree ofrichness of the weak cylinders may be the limiting factor.

In one example, cylinders receiving more than a threshold amount ofcondensate are operated rich with a degree of richness and amount ofspark advance based on the number of cylinders receiving more condensatethan the threshold amount and a number of cylinders receiving lesscondensate than the threshold amount, while cylinders receiving lessthan the threshold amount of condensate are operated lean with a degreeof leanness based on the number of cylinders receiving more condensatethan the threshold amount and the number of cylinders receiving lesscondensate than the threshold amount. As such, the sum of lean and richoperation on a given bank of cylinders may be adjusted and maintained ator near stoichiometry to maintain emissions. The degree of richness ofthe rich operating cylinders as well as the degree of leanness of thelean operating cylinders may be further based on a difference betweenthe amount of condensate received and the threshold amount. An examplefueling adjustment is shown with reference to FIG. 9.

At 320, the routine includes adjusting an engine actuator based on theincreased engine airflow (as well as the reduced torque output of thelean cylinders and the slightly elevated torque output of the richcylinders) to maintain engine torque (as such, rich for best torque(RBT) only elevates torque 1-2%). This allows engine airflow to beincreased without increasing engine torque. The adjusted engine torqueactuator may include one or more of ignition spark timing, variablecamshaft timing, and alternator load. In one example, while increasingthe engine airflow, spark timing may be advanced (e.g., advanced fromnominal MBT) in the rich operating cylinders, since they are likely tohave slower combustion due the water ingestion. As such, the slowing ofthe combustion means MBT is advanced from a nominal location at standardtesting conditions. At the same time, spark timing in the lean operatingcylinders may be maintained (e.g., maintained at MBT). The richerair-fuel ratio also helps suppress knock in the rich operated cylindersas the rate of ingestion condensation decreases as the accumulatedcondensate is consumed. Herein, the spark advance is used to trim thetorque slightly, as needed. In an alternate example, spark timing may beadvanced in all the engine cylinders during the condensate purging withmore spark advance applied to the cylinders operating rich (the weakcylinders) and less spark advance applied to the cylinders operatinglean (the strong cylinders).

It will be appreciated that in an alternate example, the condensatepurging may be performed opportunistically during a tip-in, and theincreasing engine airflow may be due to the driver tip-in. In such anembodiment, engine torque actuator adjustments may not be concurrentlyrequired and engine torque output may be allowed to increase to meet theincreased driver torque demand. However, even during the opportunisticpurging, where engine airflow is increased to or above the thresholdblow-off level responsive to a tip-in, the controller may adjust thefueling of each cylinder during the opportunistic purging based on thewater ingestion sensitivity of each individual cylinder. Specifically,while engine airflow is increased responsive to the operator pedaltip-in, cylinders with the higher water ingestion sensitivity may beenriched while the cylinders with the lower water ingestion sensitivityare enleaned with an overall exhaust air-fuel ratio maintained at oraround stoichiometry.

In this way, to compensate for the unequal condensate flow, and/or thedifferences in water ingestion sensitivity among the cylinders, duringthe condensate flow, the controller can fuel some cylinders lean whilefueling other cylinders rich while maintaining an exhaust air-to-fuelratio of the engine oscillating around stoichiometry. In particular,each cylinder of the engine may be fueled based on a water ingestionsensitivity of each cylinder. Thus, cylinders with a higher wateringestion sensitivity may be enriched while cylinders with a lower wateringestion sensitivity are enleaned. Additionally, the rich cylinders maybe run with additional spark advance to compensate for the slowedcombustion rate. The enrichment also helps in decreasing knockingtendency, when condensate consumption decays as the engine consumes thecondensate. A knock sensor output may confirm that the ingestion isending, indicating to the controller that normal operating conditionscan be restored. In one example, where the water ingestion sensitivitycorrelates with the unequal condensate distribution among the cylinders,each cylinder may be fueled based on an amount of condensate received inthe cylinder with cylinders receiving more than a threshold amount ofcondensate being enriched and spark advanced more, and cylindersreceiving less than a threshold amount of condensate being enleaned andspark advanced less. That is, to increase engine airflow withoutincreasing engine torque, spark ignition timing may be advanced forcylinders fueled rich and for cylinders fueled lean, with more sparkadvance used for the cylinders fueled rich than the cylinders fueledlean. For example, when operating the lean cylinder just lean ofstoichiometry, such as at 15:1 AFR, at least some spark advance may berequired as the burn rate may slow.

At 324, the condensate level at the CAC may be reassessed and it may bedetermined if sufficient purging has occurred. In particular, it may bedetermined if the condensate level is below a threshold level,specifically, a lower threshold level. The lower threshold level mayreflect a lower threshold of condensate storage at the CAC. Further, thelower threshold level may include some margin for hysteresis.

In an alternate example, instead of determining if the condensate levelhas dropped sufficiently, it may be determined if condensate ingestionat the cylinders has dropped (due to the condensate being consumed andno further condensate being ingested). For example, a knock signaloutput by a knock sensor may be analyzed. As discussed above, richoperation of the weak cylinders helps in decreasing knocking tendency,when condensate consumption decays as the engine consumes thecondensate. Based on the knock signal for combustion events in the richoperating (and spark advanced) cylinders, a controller may determinewhen all the condensate has been consumed. For example, in response toan increase in the knock signal and knock frequency associated with therich cylinders, it may be determined that condensate ingestion in thecylinder has been completed. Accordingly, rich operation of thecylinders may be discontinued, as discussed below.

If the condensate level is still above the threshold level (or knockingfrequency of the rich cylinders is below a threshold), at 326, theroutine includes maintaining the fueling of each cylinder based on thewater ingestion sensitivity of the cylinder while increasing engineairflow to purge condensate to the engine intake. In one example, theoperating of some cylinders rich and some cylinders lean whileincreasing the engine airflow and without increasing the engine torquemay be continued for a few seconds to complete the purging.

If the condensate level is determined to be below the (lower) thresholdlevel (or the knocking frequency of the rich cylinders is above thethreshold), then at 328, the routine includes stopping the purging ofcondensate from the CAC to the engine intake. This includes reducing theengine airflow back to a level based on the operator torque request andterminating the fueling of the cylinders based on their water ingestionsensitivity (or condensate ingestion amounts). In particular,stoichiometric fueling of the engine cylinders may be resumed.Alternatively, an alternate nominal fueling of the cylinders to providea nominal cylinder combustion air-fuel ratio based on the engineoperating conditions may be resumed. In addition, nominal spark timingmay be resumed. For example, spark timing may be returned to MBT.

Turning to FIG. 6, routine 600 depicts a method for determining thedegree of richness of the weak cylinders and adjusting the degree ofleanness of the strong cylinders in accordance. As such, the routine ofFIG. 6 may be performed as part of the routine of FIG. 3, specificallyat 316-318.

At 602, the strong cylinders having lower water ingestion sensitivitymay be identified. For example, the strong cylinder data may beretrieved from the look-up table disclosed in FIG. 5. At 604, a degreeof leanness required to increase engine airflow to a blow-off level,with degrading the combustion stability of the strong cylinders may bedetermined. For example, based on the “strength” of the cylinders, thenumber of strong cylinders, and further based on the amount of airand/or condensate expected to flow into the cylinder, a degree ofleanness of a lean fuel injection may be determined. In one example, thecontroller may use a map, such as map 800 of FIG. 8 to determine thedegree of leanness required for the cylinder based on its “strength”,the degree of leanness required increasing as the “strength” of thestrong cylinders increases. At 606, based on the determined degree ofleanness, a degree of richness required to provide an overall exhaustair-fuel ratio at or around stoichiometry is calculated. Then, at 608,the required richness is distributed between the remaining “weak”cylinders having higher water ingestion sensitivity. The requiredrichness may be distributed equally, with each of the strong cylindersreceiving fuel with the same degree of richness. Alternatively, therequired richness may be distributed unequally with each of the strongcylinders receiving a fuel injection having a richness based on eachcylinder's strength. The controller may used a map, such as map 800 ofFIG. 8 to determine the degree of richness required for each strongcylinder based on its respective “weakness”, the degree of richnessincreased as the “weakness” of the weak cylinders increases, and furtherbased on the desired richness to maintain stoichiometric exhaust.

For example, the engine may be an in-line 4 cylinder engine having oneweak cylinder and 3 strong cylinders at the time of purging. Based onthe weakness of the weak cylinder, a richness of 0.95 lambda may be usedfor the weak cylinder while the remaining strong cylinders are operatedat 1.017 lambse so that the bank is operated at essentially 1.0 lambse.Alternatively, the leanness may be distributed unequally with a firststrong cylinder operating at 1.015, a second strong cylinder operatingat 1.0125, and a third cylinder operating at 1.0135. As another example,based on the weakness of the weak cylinder, a richness of 10:1 AFR maybe determined. Accordingly, to provide an overall stoichiometric exhaust(that is, 14:1 AFR), the remaining strong cylinders may either receivean equal leanness of 16:1 AFR. Alternatively, the leanness may bedistributed unequally with a first strong cylinder operating at 16:1AFR, a second strong cylinder operating at 15:1 AFR, and a thirdcylinder operating at 15.5 AFR.

In this way, the routine of FIG. 3 (and FIG. 6) enables condensatepurging with reduced combustion issues. By operating the cylinders withhigher water ingestion sensitivity rich and with additional sparkadvance, combustion stability of cylinders most prone to misfire wheningesting condensate is reduced. By concurrently operating the cylinderswith lower water ingestion sensitivity lean, engine airflow can beraised to enable stripping of condensate from the CAC while an overallexhaust air-fuel ratio is maintained around stoichiometry. This providesemissions benefits since the stoichiometric environment maintains theexhaust catalyst active and able to convert exhaust emissions.

It will be appreciated that in an alternate embodiment of FIG. 6, thedegree of richness of the weak cylinders having higher water ingestionsensitivity may be identified first (FIG. 5) based on the “weakness” ofthe cylinders (FIG. 8), the number of weak cylinders, and further basedon combustion stability of the cylinders. A degree of leanness of thelean operating cylinders may then be adjusted based on the determineddegree of richness to provide an overall exhaust air-fuel ratio at oraround stoichiometry.

In one example, in response to elevated condensate levels, one or moreengine cylinders are operated lean so that an engine airflow isincreased, without increasing engine torque, to purge condensate from acharge air cooler to engine cylinders. Engine cylinders may be selectedfor lean operation based on their water ingestion sensitivity. Herein,the cylinders may be receiving unequal condensate amounts. A combustionair-to-fuel ratio of each engine cylinder is adjusted during the purgingbased on the amount of condensate received and a water ingestionsensitivity of each cylinder. The cylinders receiving unequal condensateamounts may include the cylinders receiving condensate amounts based onengine speed-load conditions, engine geometry, cylinder position, andcylinder firing order. Increasing engine airflow without increasingengine torque may include increasing opening of an intake throttle whileadvancing spark timing for at least the rich operating cylinders.Adjusting the cylinder combustion air-fuel ratio on acylinder-by-cylinder basis during the purging may include operating afirst engine cylinder having a water ingestion sensitivity that ishigher than a threshold at a combustion air-to-fuel ratio that is richerthan stoichiometry, and operating a second engine cylinder having awater ingestion sensitivity that is lower than the threshold at acombustion air-to-fuel ratio that is leaner than stoichiometry. Thedegree of richness of the first engine cylinder may be adjusted based onthe degree of leanness of the second engine cylinder so as to maintainan overall exhaust air-to-fuel ratio at or around stoichiometry.

In another example, in response to elevated condensate levels during anoperator tip-in, engine airflow is increased to meet torque demand andcondensate is opportunistically purged from the charge air cooler toengine cylinders. Due to the cylinders receiving unequal condensateamounts, a combustion air-to-fuel ratio of each engine cylinder isadjusted on a cylinder-by-cylinder basis during the purging based on theamount of condensate received and a water ingestion sensitivity of eachcylinder.

In another example, an engine system comprises an engine including oneor more cylinders and an intake manifold, a compressor coupled upstreamof an intake throttle, a charge air cooler coupled downstream of thecompressor, an accelerator pedal for receiving an operator torquerequest, and a controller with computer readable instructions. Theinstructions may include code for, while an accelerator pedal positionis maintained, in response to an amount of condensate stored at thecharge air cooler being higher than a threshold, increasing an openingof the intake throttle to increase airflow to the intake manifold whilemaintaining engine torque; and fueling each engine cylinder based onrespective water ingestion sensitivities while maintaining an exhaustair-to-fuel ratio at or around stoichiometry. The fueling may includerich fueling a first cylinder with a higher water ingestion sensitivityand lean fueling a second cylinder with a lower water ingestionsensitivity, a richness of the rich fueling and a leanness of the leanfueling adjusted to maintain the exhaust air-to-fuel ratio at or aroundstoichiometry. The richer cylinders may be operated at a higher level ofspark advance to maintain torque during the ingestion of the condensate,and improve robustness to knock as the rate of condensate decreases as afunction of the total condensate stored, and the rate of consumption ofthe condensate by the engine. Maintaining engine torque may alsoinclude, while increasing engine airflow, advancing spark ignitiontiming, adjusting (e.g., advancing or retarding) a variable camshafttiming and/or adjusting (e.g., increasing) an alternator load. As such.The engine airflow is increased from an initial setting to a blow-offsetting, the blow-off setting based on the amount of condensate storedat the charge air cooler.

In another example, an engine method comprises, unequally flowingamounts of condensate from a charge air cooler to among enginecylinders, and compensating for the unequal condensate flow by operatingcylinders receiving more condensate rich and cylinders receiving lesscondensate lean, with an overall exhaust air-fuel ratio maintained atstoichiometry. The method further comprises, increasing engine airflowto direct condensate from the charge air cooler to an engine intake, theincreasing engine airflow generating the unequal condensate flow. Thatis, the increasing airflow purges condensate from the CAC which isdistributed unequally along the engine cylinders due to the physicalshape of the intake manifold. Increasing engine airflow may includeadjusting a degree of leanness of the cylinders operating lean to raisean engine airflow level above a threshold level to flow condensate fromthe charge air cooler to among the engine cylinders. To increase theengine airflow, an opening of an air intake throttle may be increasedbased on the degree of leanness. An amount of condensate flowed intoeach engine cylinder is based on one or more of engine speed, enginegeometry, cylinder position on engine block, and cylinder firing order.The controller may operate cylinders receiving more condensate than athreshold amount rich, a degree of richness based on the number ofcylinders receiving more condensate than the threshold amount and anumber of cylinders receiving less condensate than the threshold amount.The controller may also operate cylinders receiving less condensate thanthe threshold amount lean, the degree of leanness further based on thenumber of cylinders receiving more condensate than the threshold amountand the number of cylinders receiving less condensate than the thresholdamount.

Now turning to FIG. 4, an example routine 400 for purging condensatefrom a CAC while adjusting fuel injection timing of engine cylinders isdepicted. The method enables at least some engine cylinders to beoperated in a lean stratified mode during condensate purging so thatsufficient mass airflow rate is provided for ingesting the condensate.The reason a controller may choose to operate one or more enginecylinders in the lean stratified mode, if available, is that thisoperation would allow the overall lean operation of the “leaner” or“stronger” cylinders, thus allowing incrementally more airflow andcondensate purging. Operating in the lean stratified mode may includeoperating the whole engine in an overall lean stratified mode, oroperating some cylinders in the lean stratified mode while operatingother cylinders in a rich mode so that an overall exhaust air-fuel ratiois maintained oscillating around stoichiometry. As such, whole engineoperation in the lean stratified mode may only be possible for a shortduration, until catalyst efficiency drops. After whole engine operationin the lean stratified mode, a period of rich operation may be requiredto restore the catalyst efficiency. The total duration of time operatedlean stratified would be determined by the oxygen storage capacity ofthe catalyst. By increasing engine airflow while adjusting the fuelinjection timing of the cylinders, condensate can be purged withoutincreasing the frequency of misfires or other combustion issues.

At 402, as at 302, the routine includes estimating and/or measuringengine operating conditions including, but not limited to, driver torquedemand (based on a pedal position), engine speed (Ne) and load, ECT,boost, ambient temperature, MAF, MAP, EGR amount, air-fuel ratio (A/F),ambient humidity, ambient pressure, BP, engine temperature, exhaustcatalyst temperature, CAC conditions (inlet and outlet temperature,inlet and outlet pressure, flow rate through the CAC, etc.) and otherparameters.

At 404, as at 304, the routine includes determining a level (or amount)of condensate stored at the CAC. As discussed at FIG. 3, the condensatelevel may be estimated based on each of mass air flow, ambienttemperature, CAC outlet temperature, CAC pressure, ambient pressure, anEGR amount, and input from a humidity sensor. The condensate levels maybe modeled based on, at 406 (as at 306) a model that computes the rateof condensate formation within the CAC based on ambient temperature, CACoutlet temperature, mass flow, EGR, humidity, etc. Alternatively, at 408(as at 308), condensate levels may be mapped to CAC outlet temperatureand a ratio of CAC pressure to ambient pressure, or CAC outlettemperature and engine load.

At 410, the determined condensate level may be compared to a thresholdlevel to determine if purging conditions have been met. The thresholdlevel may be an upper threshold of condensate storage. If the condensatelevel is not higher than the threshold level, then at 412, it may bedetermined that purging conditions have not been met and a clean outcycle is not initiated. In addition, fuel injection timing may bemaintained at a (first) fuel injection timing that provides homogeneouscylinder air-fuel charge that is ignited with spark.

If the condensate level is higher than the threshold level, then at 414,the routine includes, in response to the condensate level in the chargeair cooler, adjusting fuel injection timing while increasing engineairflow to a level greater than requested by a vehicle operator.Specifically, fuel injection timing may be shifted from the firstinjection timing providing a homogeneous cylinder air-fuel chargeignited with spark to a second injection timing providing at least somestratified cylinder air-fuel charge ignited with spark.

In particular, fuel injection timing may be adjusted so that one or moreengine cylinders are operated in a lean stratified mode. As elaboratedbelow, this may include operating some cylinders in the lean stratifiedmode while operating other cylinders at stoichiometry so that an overallexhaust air-fuel ratio is lean, or operating all cylinders in the leanstratified mode so that an overall exhaust air-fuel ratio is lean. Byoperating lean at least temporarily, the manifold airflow rate may beincreased to or above a blow off level that is sufficient to start thecondensate purging but not high enough to cause misfire and poorcombustion. In still another example, operating some cylinders in thelean stratified mode may include operating some cylinders lean whileoperating other cylinders rich so that an overall exhaust air-fuel ratio(received at an exhaust three-way catalyst, for example) is at or aroundstoichiometry (e.g., oscillates around stoichiometry).

Adjusting the fuel injection timing from the first timing to the secondtiming may include, for example at 416, adjusting a number of fuelinjections per cylinder combustion event. The adjusting may alsoinclude, for example at 418, shifting from the first injection timingincluding an intake stroke injection to the second injection timingincluding a compression stroke injection. As used herein, the intakestroke injection may include any one of an early intake stroke injection(e.g., one that starts late in the exhaust stroke and ends early in theintake stroke), a mid intake stroke injection (e.g., one that starts andends in the intake stroke) and a late intake stroke injection (e.g., onethat starts in the intake stroke and ends in the compression stroke),and wherein the compression stroke injection includes a late compressionstroke injection.

In one example, the controller may transition the fuel injection timingfrom a single intake stroke fuel injection to a split fuel injectionincluding at least a compression stroke injection. The number ofmultiple injections may be based on the condensate level. For example,as condensate level exceeds the threshold level, the controller mayadjust the fuel injection timing to increase a number of fuel injectionsper engine cycle, and increase a ratio of fuel delivered in acompression stroke relative to an intake stroke. The split ratio mayalso be determined by the amount of leanness required. For example,induction injection (intake stroke injection) may be used to schedule anoverall lean operation, while compression injection may be used close tospark ignition to maintain a relatively combustible mixture around thespark plug.

Shifting the fuel injection timing may further include adjusting theinjection timing of all the cylinders with the timing of “strong”cylinders having a lower water ingestion sensitivity (or those ingestingless condensate) in the lean stratified mode while adjusting theinjection timing of the “weak” cylinders having a higher water ingestionsensitivity (or those ingesting more condensate) in a rich mode suchthat an overall exhaust air-fuel ratio is maintained at or aroundstoichiometry with at least the rich cylinders operated with additionalspark advance. As discussed with reference to FIG. 3, the wateringestion sensitivity of the cylinders may be predetermined duringengine testing and stored in a look-up table (such as the table of FIG.5) in the controller's memory.

In an alternate example, instead of operating cylinders having lowerwater ingestion sensitivity in the lean stratified mode while operatingcylinders having higher water ingestion sensitivity in a rich mode withan overall exhaust air-fuel ratio maintained around stoichiometry,shifting the fuel injection timing may include operating cylindershaving lower water ingestion sensitivity in the lean stratified modewhile operating cylinders having higher water ingestion sensitivity in astoichiometric mode with an overall exhaust air-fuel ratio maintainedlean. By not operating the weak cylinders lean, the likelihood ofcondensate ingestion induced misfires in the weak cylinders is reduced.

As such, the lean stratified mode injection timing for the selectedcylinders may be adjusted so that a richer air-fuel ratio is provided inthe vicinity of the spark plug while providing an overall lean air-fuelratio in the cylinder. By providing a rich air-fuel ratio around thespark plug, a more stable combustion is enabled. By providing an overalllean cylinder combustion air-fuel ratio, the manifold air flow rate israised sufficiently high to enable purging of the condensate to beinitiated.

At 422, a degree of leanness of the lean stratified operation may beadjusted to increase engine airflow to or above the blow-off level thatenables condensate purging. That is, by operating in the lean stratifiedmode, engine airflow level is increased based on the condensate level inthe charge air cooler. The engine airflow level is then increased to ablow-off level required to purge condensate from the charge air cooler.By raising the airflow rate, a condensate airflow stripping velocity inthe CAC is raised, which purges the condensate into the engine.

The degree of leanness may be further based on the susceptibility of thecylinders to receive condensate. This is because condensate may not comeout evenly from the CAC into the engine cylinders. Specifically, duringthe purging, more condensate may come out at an initial part of thepurging while less condensate may be come out at a later part of thepurging. To address this unequal release of condensate, the controllermay track the cylinder firing order so that cylinders firing during theinitial part of the purging (e.g., immediately after purging is startedor earlier in the cylinder firing order), which are more likely toreceive more condensate, are adjusted to have a lower degree of leannesswhile cylinders firing during the later part of the purging (e.g.,sometime after purging is started or later in the cylinder firingorder), which are more likely to receive less condensate, are adjustedto have a higher degree of leanness.

For example, certain cylinders may be more prone to getting thecondensate. By estimating the transport delay time for the condensate toget from the CAC to the “prone” cylinders, and further based on how muchcondensate has accumulated (e.g., modeled or measured), and how much hasbeen consumed, the controller may estimate the number of affectedcombustion cycles and the decay rate to adjust accordingly.Alternatively, the controller may use the knock sensor output asfeedback to determine when the condensate has purged, and when to returnair, fuel and spark control back to normal levels. For example, inresponse to an increase in knocking frequency in the rich operatedcylinders, completion of condensate ingestion may be determined.

A degree of richness of the remaining cylinders is then adjusted basedon the degree of leanness so that an overall exhaust air-fuel ratio ismaintained around stoichiometry. By providing stoichiometric exhaust toa downstream emission control device, an exhaust catalyst can be keptcatalytically active, providing improved emissions performance.

As elaborated below at FIG. 7, the adjusting may include firstdetermining the degree of leanness required to operate the strongcylinders in the lean stratified mode and then adjusting the degree ofrichness of the weak cylinders to provide an overall stoichiometricexhaust air-fuel ratio (or lean exhaust air-fuel ratio, as required). Inother words, the degree of leanness of the weak cylinders may be thelimiting factor. This is because operation in the lean stratified modemay require a threshold degree of leanness. Thus, it may be requiredthat the strong cylinders are operated with a degree of leanness that iswithin the lean stratified mode limit. The degree of leanness may alsobe determined by the airflow increase needed to strip the condensate andmaintain torque output.

At 424, as at 324, the condensate level at the CAC may be reassessed andit may be determined if sufficient purging has occurred. In particular,it may be determined if the condensate level is below a threshold level,specifically, a lower threshold level. The lower threshold level mayreflect a lower threshold of condensate storage at the CAC. Further, thelower threshold level may include some margin for hysteresis. If thecondensate level is still above the threshold level, at 426, the routineincludes continuing engine operation with the injection timing shiftedto the second timing that provides lean stratified combustion withspark. In one example, the operating at least some cylinders in the leanstratified mode may be continued for a few seconds to complete thepurging.

If the condensate level is determined to be below the (lower) thresholdlevel, then at 428, the routine includes stopping the purging ofcondensate from the CAC to the engine intake. This includes returningfuel injection timing to the first injection timing and resuminghomogeneous combustion of cylinder air-fuel charge with spark.

Turning to FIG. 7, routine 700 depicts a method for determining thedegree of leanness of the strong cylinders and adjusting the degree ofrichness of the weak cylinders in accordance. As such, the routine ofFIG. 7 may be performed as part of the routine of FIG. 4, specificallyat 422.

At 702, the strong cylinders having lower water ingestion sensitivitymay be identified. For example, the strong cylinder data may beretrieved from the look-up table disclosed in FIG. 5. At 704, a(minimum) degree of leanness required to operate the strong cylinders inthe lean stratified mode may be determined. For example, based on thestrength of the cylinder, a degree of leanness of a lean fuel injectionmay be determined. In one example, the controller may use a map, such asmap 850 of FIG. 8 to determine the degree of leanness required for thecylinder based on its “strength”, the degree of leanness requiredincreasing as the “strength” of the strong cylinders increases. At 706,the determined degree of leanness is compared to a limit of the leanstratified mode. For example, the determined degree of leanness may becompared to a lower leanness threshold or limit of operation in the leanstratified mode. If the determined degree of leanness is not within thelimit (e.g., it is richer than the limit), then at 707, the routineincludes readjusting the determined degree of leanness to be at the leanstratified mode limit. After readjusting, or if the determined degree ofleanness is already within the lean stratified mode limit, at 708, basedon the determined degree of leanness, a degree of richness required toprovide a desired exhaust air-fuel ratio (e.g., overall at or aroundstoichiometry or overall leaner than stoichiometry) is calculated. Then,at 710, the required richness is distributed between the remaining“weak” cylinders having higher water ingestion sensitivity. The requiredrichness may be distributed equally, with each of the weak cylindersreceiving fuel with the same degree of richness. Alternatively, therequired richness may be distributed unequally with each of the weakcylinders receiving a fuel injection having a richness based on eachcylinder's weakness. The controller may used a map, such as map 800 ofFIG. 8 to determine the degree of richness required for each weakcylinder based on its respective “weakness”, the degree of richnessincreased as the “weakness” of the weak cylinders increases, and furtherbased on the desired richness to provide the desired overall exhaustair-fuel ratio. Likewise, similar to map 800, the additional spark maybe mapped to the weakness of the weak cylinders, and the propensity ofthe cylinders to receive condensate may be used to estimate the sparkadvance required to restore combustion to optimal phasing.

For example, the engine may be an in-line 4 cylinder engine having onestrong cylinder and 3 weak cylinders at the time of purging. Based onthe strength of the strong cylinder, a leanness of 1.3 lambse may bedetermined. As such, this value may be within a lean stratified modelimit (of 1.5 lambse). Accordingly, to provide an overall stoichiometricexhaust (AFR=1.0), the remaining weak cylinders may either receive anequal richness of 0.9 lambse. Alternatively, the richness may bedistributed unequally with a first weak cylinder operating at 0.8lambse, a second weak cylinder operating at 0.9 lambse , and a thirdweak operating at 1.0 lambse. In another example, based on the strengthof the strong cylinder, a leanness of 16:1 AFR may be determined. Assuch, this value may be within a lean stratified mode limit (of 17:1AFR). In another example, depending on the engine combustion chamberdesign, a lean stratified limit of˜30:1 AFR may be applied because thecompression injection near the spark plug is rich enough for combustionwhile the overall air-fuel ratio remains very lean. Accordingly, toprovide an overall stoichiometric exhaust (14:1 AFR), the remaining weakcylinders may either receive an equal richness of 11:1 AFR.Alternatively, the richness may be distributed unequally with a firstweak cylinder operating at 10.5:1 AFR, a second weak cylinder operatingat 11.0:1 AFR, and a third weak operating at 11.0:1 AFR.

In this way, the routine of FIG. 4 (and FIG. 7) enables condensatepurging with reduced combustion issues. By temporarily operating atleast the cylinders with lower water ingestion sensitivity in a leanstratified mode, manifold airflow rate can be sufficiently increased toblow off condensate to the cylinders without inducing misfires. Byoptionally adjusting the fuel injection timing of the cylinders that aremost prone to misfire to operate rich, combustion issues in thosecylinders during the purging can be reduced. By maintaining an overallexhaust air-fuel ratio around stoichiometry, emissions benefits areachieved.

In one example, a controller may purge condensate from a charge aircooler while temporarily shifting cylinder combustion to a leanstratified mode, a degree of enleanment based on an amount of condensateat the charge air cooler and a cylinder firing order during the purging.Temporarily shifting cylinder combustion to a lean stratified mode mayinclude shifting combustion in (only) a first cylinder having a lowerwater ingestion sensitivity to the lean stratified mode. Optionally,while shifting combustion in the first cylinder to the lean stratifiedmode, combustion in a second cylinder having a higher water ingestionsensitivity may be shifted to a rich mode and operated at a moreadvanced spark placement such that an overall exhaust air-fuel ratio ismaintained around stoichiometry, and the spark placement maintains theoptimal burn rate. A degree of enleanment may be adjusted to provide anengine airflow that is higher than a threshold level (e.g., blow-offlevel), the threshold level based on the amount of condensate at thecharge air cooler. The degree of enleanment may be further based on alean stratified mode leanness limit, the degree of enleanment adjustedto be within the limit, the degree of enrichment then adjusted based onthe degree of enleanment to provide stoichiometric exhaust. One or moreof the degree of enleanment and a duration of operating in the leanstratified mode may be increased as the amount of condensate increasesabove a threshold amount. Temporarily shifting to the lean stratifiedmode may also includes shifting from a homogeneous mode where fuel isinjected at least in an intake stroke to the lean stratified mode wherefuel is injected at least in a compression stroke. Further still, thecontroller may performing a split fuel injection and increase a numberof fuel injections per engine cycle based on the amount of condensate atthe charge air cooler.

In another example, an engine system comprises an engine including oneor more cylinders, a compressor coupled upstream of an intake throttle,a charge air cooler coupled downstream of the compressor, a direct fuelinjector for injecting fuel into an engine cylinder, and a controllerwith computer readable instructions. The computer may include code for,while an accelerator pedal position is maintained, in response to acondensate level at the charge air cooler being higher than a threshold,adjusting an engine fuel injection timing to operate one or morecylinders in a lean stratified mode until the condensate level is belowthe threshold. The adjusting may include operating cylinders havinglower water ingestion sensitivity in the lean stratified mode whileoperating cylinders having higher water ingestion sensitivity in astoichiometric mode with an overall exhaust air-fuel ratio maintainedlean for a period of time determined by the catalyst oxygen storagecapacity, followed a period of rich operation after the condensate isconsumed to return the oxygen storage balance and efficiency in thecatalyst. Additionally, the adjusting may include operating cylindershaving lower water ingestion sensitivity in the lean stratified modewhile operating cylinders having higher water ingestion sensitivity in arich mode with an overall exhaust air-fuel ratio maintained aroundstoichiometry.

Now turning to FIG. 9, map 900 depicts an example condensate purgingoperation wherein fuel injection and combustion air-fuel ratios ofcylinders are individually adjusted based on respective water ingestionsensitivities. The approach allows condensate purging with reducedoccurrence of cylinder misfires. Map 900 depicts condensate levels atthe CAC at plot 902, air intake throttle position at plot 904, fuelinjection changes at 905-906, an overall exhaust air-fuel ratio (sensednear an exhaust emission control device) at plot 908, spark timingadjustments at plot 910, and engine torque at plot 912. Plot 914 depictsthe output of a knock sensor while plot 916 depicts an intake manifoldairflow.

Prior to t1, condensate may be accumulating during engine operation atthe charge air cooler (plot 902). The engine may be operating prior tot1 with fuel injection to each cylinder adjusted to providestoichiometric cylinder combustion (see block 905 relative to dashedline) and with spark timing at MBT (plot 910). A throttle opening (plot904) and fuel injection amount may be adjusted to provide an engineairflow that corresponds to a torque output (plot 912) that meets thedriver torque demand. Also, prior to t1, the engine may not be knocking.

At t1, condensate levels may reach an upper threshold 901 triggeringpurging conditions. At t1, in response to the elevated condensate level,cylinder fueling may be adjusted so that one or more engine cylindersare operated leaner than stoichiometry. In the depicted example, threecylinders may be operated lean while one cylinder is operated rich (seeblocks 906 relative to dashed line). The controller may maintain fuelinjection to the lean cylinders while increasing engine airflow to thecylinders to provide the desired leanness. In particular, the degree ofleanness may of the lean operating cylinders may be adjusted so that theengine airflow level (MAP, plot 916) is increased to or above athreshold level 917 where condensate can be stripped from the charge aircooler and purged into the engine intake. The throttle opening may beincreased to increase engine airflow and provide the requisite degree ofleanness. As such, the water ingestion sensitivity of the cylinders mayvary. Therefore the controller may advantageously select the strongcylinders having lower water ingestion sensitivity for operating lean(to provide the increased engine airflow) while selecting the remainingweak cylinders having higher water ingestion sensitivity for operatingrich (to enable air-fuel ratio control). In addition, since theincreased engine airflow may flow condensate from the CAC into theengine, but unequally to the engine cylinders (with some receiving morecondensate than others), by adjusting the cylinder fueling based on theinherent variation in cylinder sensitivity to water ingestion, theunequal condensate flow may be compensated for.

Specifically, the weak cylinders (herein one cylinder) having higherwater ingestion sensitivity may be operated rich while the remainingstrong cylinders (herein three cylinders) having lower water ingestionsensitivity may be operated lean. The degree of leanness of the strongcylinders may be adjusted based on the condensate level at the CAC toincrease the engine airflow level (plot 916) above threshold 917. Thedegree of richness of the remaining cylinders is then adjusted based onthe degree of leanness of the weak cylinders to maintain an overallexhaust air-fuel ratio (AFR) at stoichiometry (see dashed line). In thedepicted example, the degree of leanness of the strong cylinders isadjusted unequally, with each cylinder adjusted based on its strength,the stronger the cylinder, the higher the degree of leanness tolerated(see three hatched blocks below dashed stoichiometric line).

To maintain the engine torque output while fueling the cylindersdifferently, as well as to reduce the knocking frequency of the weakcylinders ingesting condensate, the cylinder operating rich may also beoperated with spark timing advanced from MBT, as shown at plot 910. Atthe same time, the cylinders operating lean may be operated with nominalspark timing maintained, as shown at dashed plot 911. In alternateexamples, the rich cylinders may have more spark advance while the leancylinders have less spark advance.

As such, engine operation with fueling as per 906 may be continued for anumber of engine cycles and the condensate level may start falling fromupper threshold 901. At t2, the condensate level may be at or belowlower threshold level 903 indicating that the condensate has beensufficiently purged from the CAC. In addition, due to consumption of thecondensate in the engine, the rich operating (weak) cylinders may startto knock. As shown at plot 914, just before t2, the knocking frequencyof the rich cylinders may be increase, and the output of a knock sensorcoupled to the rich cylinders may frequently exceed knock threshold 915.In response to the sudden increase in knock frequency, the controllermay infer than condensate consumption has been completed. Accordingly,at t2, original settings of engine airflow, fueling and ignition timingmay be resumed. Specifically, the throttle opening may be decreased to anominal position based on engine operating conditions. Also, sparktiming may be returned to MBT. Further, engine operation may be resumewith fueling as per 905 (stoichiometric cylinder combustion).

It will be appreciated that while the above example actively increasesthe engine airflow without increasing engine torque responsive to thecondensate level to enable purging, in an alternate example, thecondensate may be opportunistically purged during a tip-in while takingadvantage of the increased engine airflow of the tip-in. For example, inresponse to a tip-in occurring at t1 (or shortly after t1), the intakethrottle opening may be increased (plot 904) to provide the engineairflow required to meet the increased torque demand. In addition, sparktiming may be maintained at MBT (see dotted segment 911) so that enginetorque can be increased based on driver demand (see dotted segment 913).While the condensate is opportunistically purged, the fuel injection tothe cylinders may be shifted to the cylinder-by-cylinder basis (as per906) so that combustion stability issues of each cylinder can beaddressed when ingesting condensate during the purging. At t2,responsive to a tip-out the engine airflow may be decreased.

In this way, condensate can be purged without degrading combustion inengine cylinders and while reducing the frequency of ingestion inducedmisfires.

Now turning to FIG. 10, map 1000 depicts an example condensate purgingoperation wherein fuel injection timing and mode of combustion ofcylinders are adjusted to provide an engine airflow that enablescondensate blow-off without increasing the occurrence of cylindermisfires. Map 1000 depicts an air-fuel ratio of engine cylinders at plot1002 wherein air-fuel ratios to the right of the y-axis depictincreasing degree of richness while air-fuel ratios to the left of they-axis depict increasing degree of leanness. A leanness range requiredfor cylinder operation in a lean stratified mode is shown at 1004(shaded block).

In the depicted example, the engine is an in-line four cylinder enginehaving three weak cylinders (W1-W3) and one strong cylinder (S1). Inresponse to elevated condensate levels, condensate purging may berequested. Therein, to provide the engine airflow required to blow offthe condensate, one or more engine cylinders may need to be operated ina lean stratified mode. In the depicted example, the strong cylinder S1having the lower water ingestion sensitivity may be selected foroperation in the lean stratified mode. Based on the condensate level inthe CAC, a degree of leanness for S1 is determined.

Herein, the determined degree of leanness may be within lean stratifiedmode limit 1004, and therefore permissible. Thus, S1 is operated in thelean stratified mode with the determined degree of leanness. At the sametime, weak cylinders W1-3 are operated in a rich mode with a degree ofrichness adjusted based on the leanness of S1 so that an overall exhaustair fuel ratio is maintained at stoichiometry. Herein, the degree ofrichness of cylinders W1-3 are adjusted based on their “weakness” withthe less weak cylinders W1 and W2 being enriched less and the more weakcylinder W3 being enriched more. By operating S1 in the lean stratifiedmode, the increased engine airflow can be used to purge the condensatewhile lean operation is used in the cylinder that tolerates the mostcondensate ingestion to reduce the potential for misfires. At the sametime, rich operation is used in the cylinders that do not toleratecondensate ingestion well to improve combustion stability in thecylinders and reduce the potential of misfires in those cylinders.

As such, the degree of richness of the weak cylinders may be adjustedwithin a range. Specifically, if a weak cylinder is enriched too much,this could result in late combustion that could turn into misfire withthe addition of the condensate. Thus, the weak cylinders with the leastwater ingestion are likely operated richest, with the weakest cylindergetting the most condensate operated the least rich, possible past RBT(rich for best torque) while still maintaining overall stoichiometricair-fuel ratio at the exhaust catalyst.

In an alternate example, the degree of leanness the strong cylinder(herein S1′ depicted in dashed lines) may be determined to be outside oflean stratified mode limit 1004. Specifically, the required leanness maybe less lean than a minimum amount of leanness required to operate inthe lean stratified mode (see S1′ outside of shaded block 1004). In sucha scenario, the degree of leanness of S1′ is adjusted to lie within orat the lean stratified mode limit. For example, as shown by the arrow,the degree of leanness for S1′ may be increased more than required sothat the leanness falls within the leanness required for operation inthe lean stratified mode. To compensate for the added leanness, one ormore of the weak engine cylinders may have their degree of richnessincreased. In the depicted example, as shown by the arrow, the degree ofrichness of W3 may be increased to compensate for the increase inleanness of S1′.

In another example, in response to condensate level in a charge aircooler, a controller may adjust fuel injection of each engine cylinderbased on a water ingestion sensitivity of each cylinder to increase anengine airflow above a threshold level while maintaining an overallexhaust air-fuel ratio around stoichiometry. The adjusting may include,enleaning one or more engine cylinders having lower water ingestionsensitivity, a degree of leanness adjusted to increase the engineairflow above the threshold level, and enriching remaining enginecylinders having higher water ingestion sensitivity, a degree ofrichness adjusted based on the degree of leanness to maintain theexhaust air-fuel ratio around stoichiometry. The adjusting may beperformed in response to condensate level in the charge air cooler beinghigher than a threshold amount. The threshold (airflow) level abovewhich the engine airflow is increased may be is based on a differencebetween the condensate level in the charge air cooler and the thresholdamount. Thus, as the condensate level at the CAC increases, a degree ofleanness of the lean operating cylinders may be increased to accordingfurther raise the engine airflow level. The degree of richness of therich operating cylinders may then be adjusted in accordance to maintainan overall stoichiometric exhaust air-fuel ratio.

In this way, condensate may be periodically cleaned from a charge aircooler by blowing off condensate to the engine cylinders. By adjustingthe fueling of each cylinder during the condensate purging and the sparkadvance to cylinders receiving a majority of the condensate, based oneach cylinder's water ingestion sensitivity, and/or the amount ofcondensate ingested, variations in cylinder combustion stability andmisfire occurrence can be compensated for. By operating cylinders thatare more prone to condensate induced combustion issues richer thanstoichiometry, combustion stability of those cylinders during purging isimproved. By operating other cylinders that are less prone to condensateinduced combustion issues leaner than stoichiometry, an overallstoichiometric environment can be provided in the exhaust, improvingengine performance and exhaust emissions. By adjusting fuel injectiontiming so that at least one or more strong cylinders are operated in alean stratified mode, an engine airflow level can be sufficientlyincreased to initiate condensate purging. By using a stratifiedinjection mode that maintains a rich environment in the vicinity of acylinder's spark plug, combustion stability is improved. Overallcondensate purging is enabled while reducing combustion issues relatedto condensate ingestion.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein. Thefollowing claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereofSuch claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. An engine method, comprising: in response to condensate level in acharge air cooler, adjusting fuel injection timing while increasingengine airflow to a level greater than requested by a vehicle operator.2. The method of claim 1, wherein adjusting fuel injection timingincludes shifting from a first injection timing providing a homogeneouscylinder air-fuel charge ignited with spark to a second injection timingproviding at least some stratified cylinder air-fuel charge ignited withspark.
 3. The method of claim 2, wherein the first injection timingincludes an intake stroke injection and wherein the second injectiontiming includes a compression stroke injection.
 4. The method of claim3, wherein the intake stroke injection includes one of an early intakestroke injection, a mid intake stroke injection and a late intake strokeinjection, and wherein the compression stroke injection includes a latecompression stroke injection.
 5. The method of claim 4, whereinadjusting fuel injection timing further includes adjusting a number offuel injections per combustion event.
 6. The method of claim 5, whereinadjusting the number of fuel injections includes transitioning from asingle intake stroke fuel injection to a split fuel injection includingat least a compression stroke injection.
 7. The method of claim 1,wherein adjusting fuel injection timing includes, as condensate levelexceeds a threshold, increasing a number of fuel injections per enginecycle, and increasing a ratio of fuel delivered in a compression strokerelative to an intake stroke.
 8. The method of claim 1, wherein theincreased engine airflow level is based on the condensate level in thecharge air cooler.
 9. The method of claim 1, wherein in response to acondensate level in the charge air cooler includes in response to thecondensate level being higher than a threshold level.
 10. The method ofclaim 1, wherein adjusting to increase engine airflow level includesadjusting to increase engine airflow level to a blow-off level requiredto purge condensate from the charge air cooler.
 11. An engine method,comprising: purging condensate from a charge air cooler whiletemporarily shifting cylinder combustion to a lean stratified mode, adegree of enleanment based on an amount of condensate at the charge aircooler and a cylinder firing order during the purging.
 12. The method ofclaim 11, wherein temporarily shifting cylinder combustion to a leanstratified mode include shifting combustion in a first cylinder having alower water ingestion sensitivity to the lean stratified mode.
 13. Themethod of claim 12, further comprising, while shifting combustion in thefirst cylinder to the lean stratified mode, shifting combustion in asecond cylinder having a higher water ingestion sensitivity to a richmode such that an overall exhaust air-fuel ratio is maintained aroundstoichiometry.
 14. The method of claim 13, wherein the degree ofenleanment is adjusted to provide an engine airflow that is higher thana threshold level, the threshold level based on the amount of condensateat the charge air cooler.
 15. The method of claim 14, wherein the degreeof enleanment is further based on a lean stratified mode leanness limit,the degree of enleanment adjusted to be within the limit, and whereinthe degree of enrichment is adjusted based on the degree of enleanmentto provide stoichiometric exhaust.
 16. The method of claim 12, whereinone or more of the degree of enleanment and a duration of operating inthe lean stratified mode is increased as the amount of condensateincreases above a threshold amount.
 17. The method of claim 13, whereintemporarily shifting to the lean stratified mode includes shifting froma homogeneous mode where fuel is injected at least in an intake stroketo the lean stratified mode where fuel is injected at least in acompression stroke.
 18. The method of claim 14, wherein temporarilyshifting to the lean stratified mode further includes performing a splitfuel injection and increasing a number of fuel injections per enginecycle based on the amount of condensate at the charge air cooler.
 19. Anengine system, comprising: an engine including one or more cylinders; acompressor coupled upstream of an intake throttle; a charge air coolercoupled downstream of the compressor; a direct fuel injector forinjecting fuel into an engine cylinder; and a controller with computerreadable instructions for, while an accelerator pedal position ismaintained, in response to a condensate level at the charge air coolerbeing higher than a threshold, adjusting an engine fuel injection timingto operate one or more cylinders in a lean stratified mode until thecondensate level is below the threshold.
 20. The system of claim 19,wherein the adjusting includes operating cylinders having lower wateringestion sensitivity in the lean stratified mode while operatingcylinders having higher water ingestion sensitivity in a stoichiometricmode with an overall exhaust air-fuel ratio maintained lean, oroperating cylinders having lower water ingestion sensitivity in the leanstratified mode while operating cylinders having higher water ingestionsensitivity in a rich mode with an overall exhaust air-fuel ratiomaintained around stoichiometry.